Recently, with the rapid development of data services, the Ethernet technology has been used widely in the Metropolitan Area Networks (MAN), since it has some advantages, such as low cost, simple structure, as well as facilitations of transmitting and processing Internet Protocol (IP) data packets. However, the Ethernet technology can not effectively meet the current requirement of a MAN in the aspects of reliability and expansibility, since it lacks the Quality of Service (QoS) of the telecommunication level and the network management mechanism for fast protection/recovery and integrity. Hence, the RPR technology emerges as required.
RPR is a Multi-Service Transmission Platform (MSTP) technology that transmits services, e.g. data, voice, image, etc, by using the packet technology in a ring network structure. Integrating the intelligence of IP technology, the economical efficiency of the Ethernet and the high bandwidth efficiency as well as reliability of an optical ring network, RPR solves the QoS problems, such as the classification of service, and provides a favorable networking solution for the broadband IP MAN operators.
As shown in FIG. 1, the RPR adopts a dual-ring architecture that is composed of an external ring and an internal ring, wherein the transporting direction of the internal ring is opposite to that of the external ring; hence two transmission paths exist between a pair of nodes. In addition, when all of the nodes in the RPR are Layer3 data communication devices, e.g. Layer3 switches and routers, the packets transmission between the Layer3 devices may be implemented; when all of the nodes in the RPR are Layer2 data communication devices, e.g. Layer2 switches, the packets transmission between the Layer2 devices may be implemented.
In accordance with RPR protocols, the RPR implements communications between Layer2 devices by using the bridge mode. Specifically, the nodes in the RPR convert an insert packet came from a User Equipment (UE) to an extended frame-formatted packet and broadcasts it on the whole network. The nodes that receive the extended frame-formatted packet convert the packet to an Ethernet frame-formatted packet and send the Ethernet frame-formatted packet to the UE connected with it.
As shown in FIG. 2, the method for transporting a packet between Layer2 devices in an existing RPR includes the following steps:
Step 201: A node of the RPR receives an insert packet came from a UE.
Steps 202˜203: The nodes that receive the insert packet convert the format of the packet from the Ethernet frame format to the RPR extended frame format, and broadcast the converted packet to the whole network.
Generally, the format of the insert packet received by an RPR node is the Ethernet frame format. However, the packet transported in the RPR must conform to the RPR protocols. Thus, the node that receives the insert packet needs to perform the format conversion for the packet.
In accordance with the RPR protocols, the format of the packet transported in the RPR may be an RPR basic frame format or the RPR extended frame format. The RPR basic frame format is used in an RPR that is composed of Layer3 devices while the RPR extended frame format is used in an RPR that is composed of Layer2 devices. Table 1 shows the specific architecture of the RPR extended frame.
TABLE 1Length(Byte)FieldIndication1TTLTime To Live (TTL), indicates themaximal number of hops and issubtracted 1 each time the packetpasses one node in the forwardingprocess1BaseControlRPR frame control message6R_DmacMAC address of RPR destination node6R_SmacMAC address of RPR source node1TTLBaseoriginal value of the Maximal numberof hops of the RPR frame, remainsunchanged in the forwarding process1ExtendedControlRPR extended frame control field2HECHead error check6DmacExtendedExtended destination MAC address,i.e. MAC address of the destinationUE, the actual destination MACaddress of the Ethernet frame6SmacExtendedExtended source MAC address, i.e.MAC address of the source UE, theMAC address of the UE that initiatesthe Ethernet frameDataRemaining frame data4FCSFrame Check Sequence
A Layer3 device can identify the source IP address and the destination IP address carried in a packet, and need not use the Media Access Control (MAC) address to transmit and receive the packet. Thus the basic frame format used in the RPR that is composed of Layer3 devices does not have the two fields of SmacExtended and DmacExtended, compared with the extended frame format in the table 1.
Herein, when an Ethernet insert packet is converted to an RPR extended frame-formatted packet, the source MAC address carried in the packet is used as the SmacExtended field of the extended frame, the destination MAC address is used as the DmacExtended field of the extended frame, the MAC address of the node receiving the insert packet is used as the R_Smac field, and the broadcast MAC address is used as the R_Dmac field.
Upon completing the conversion of the insert packet from the Ethernet frame format to the extended frame format, the node receiving the insert packet sends out the converted packet by the way of broadcasting on the whole network.
Steps 204˜205: The nodes that receive the extended frame-formatted packet convert the format of the received packet to the Ethernet frame format, and determine the way of processing the packet according to the destination MAC address of the packet.
When the extended frame-formatted packet arrives at a node of the RPR, the format of the packet is converted from the extended frame format to the Ethernet frame format. The detailed method includes: removing the HEC field, the R_Dmac field, the R_Smac field and the BaseControl field of the extended frame-formatted packet, and using the MAC address indicated by the DmacExtended field as the destination MAC address of the Ethernet frame-formatted packet.
Then, according to the destination MAC address of the packet, the node receiving the packet checks if itself is connected with the destination UE of the packet or not. If it is connected with the destination UE, the node sends the Ethernet frame-formatted packet towards the UE corresponding to the destination MAC address; otherwise, processes the Ethernet frame-formatted packet according to the network configuration, e.g. discards the packet.
By now, the packet transmission process in the existing RPR network is completed.
As the broadcast mode is used in the packet transmission in the existing RPR networks, i.e. the extended frame-formatted packet, after being inserted in the ring from the source node, is respectively sent to the other nodes in the RPR except for the source node, the ring paths between the source node and the other nodes of the RPR are largely used, thereby occupying larger bandwidth and requiring more communication resources.